The Relative Food Value of Diatoms, Dinoflagellates, Flagellates, and Cyanobacteria for Tintinnid Ciliates

Arch. l'rotistenkd. (1986) 131: 71-84 VEB Gustav Fischer Verlag Jena

Graduate Kchool of Oceanography, l.~nivcrsity of Hhode Island, Kingston, Hhode Island, e.S.A.

The Relative Food Value of Diatoms, Dinoflagellates, Flagellates, and Cyanobacteria for Tintinnid Ciliates By PETER G. VERITY and TRACY A. VILLAREAL With 4 Figures Key words: tintinnids; phytoplankton; chitin threads

Summary Growth rates of two coastal tintinnid ciliates, Tintinnopsis acuminata DADAY and Tintinnopsis 't'oscllium MEUNIER, were measured in batch cultures of 10 diatom clones, 10 clones of dinoflagellates and flagellates, and 2 clones of chroococcoid cyanobacteria. Diatom clones represented species lacking significant external processes (Min utocellus), species possessing siliceous setae (Chaetoceros), and species possessing {i.chitin threads (Thalassiosil'fl, Cyclotella). Both tintinnids grew rapidly when fed diatoms lacking threads or setae; neither species grew when fed setae-bearing diatoms. The smaller tintinnicl, 'l'intinnopsis acumina/a, exhibited extensive mortality when fed t hread- bearing diatoms; the larger tintinnid, Tintinnopsis v((sculum, grew only when fed the two smallest thread-bearing diatoms. Both tintinnids grew rapidly on diatoms with threads reduced by culture on a shaker table: growth rates were inversely related to diatom cross-sectional diameter (~ cell + threads). Tintinnids feeding on the prymnesiophytes, Dicrateria, Isochrysis, and Pavlova, grew at rates similar to those feeding on diatoms lacking significant external processes. T. vClsculum showed moderate growth whEn fed dinoflagellates, while T. llcuminata grew well when fed chlorophytes and prasinophytes. Both tintinnids !'xhibitecl extensive mortality when fed the chroococcoid cyanobacteria, Synechococcus.

Introduction Microzooplankton function as an intermediate link in the transfer of nanoplankton production to higher trophic levels (PARSONS and LEBRASSEUR 1970; PORTER et al. 1979). They graze phytoplankton too small to be efficiently filtered by macrozooplankton (NIVAL and NIVAL 1976) and translate that production into a size class available to larger herbivores (BERK et al. 1977; ROBERTSON 1983). Culture work, predominantly on tintinnid ciliates, has supported the potential importance of flagellates as food for protozoan microzooplankton (GOLD 1971, 1973; BLACKBOURN 1974; HEINBOKEL 1978a). Diatoms may not be an important component of the diet of microzooplankton because most diatom species are too large in diameter or chain length to be ingested (BLACKBOURN 1974). Quantitative data on the food value of diatoms are lacking, alt.hough JOHANSEN (1976) reported that tintinnids could not be maintained in culture on a pure diet of diatoms. Diatoms are a regular component of the diet of marine benthic ciliates (FENCIIEL 1968). Small, solitary centric diatoms identified as 'l'halassiosira and Cyclotella species grow rapidly in situ throughout the summer in Narragansett Bay (FURNAS 1982)

72

P. G. VERITY and T. A. VILLAREAL

where major blooms occur in late fa]) (VERITY 1984). These species were too small (5-10 /Lm) to be efficiently grazed by Acartia (NIVAL and NIVAL 1976), the dominant copepod in the bay, suggesting that microzooplankton might be important consumers of these phytoplankton. Tintinnids are the numerically dominant ciliate microzooplankton in Narragansett Bay (VERITY 1984), but in situ growth rates of natural tintinnid populations are unusually low during blooms of small Thalassiosira species (VERITY 1984). GIFFORD et al. (1981) hypothesized that the presence of j1-chitin threads in Thalassiosira weiss/logii (GRUNOW) G. FRYXELL and HASLE may increase effective diatom cell size, reducing grazing by microzooplankton. Preliminary laboratory experiments indicated that tintinnids isolated from Narragansett Bay did not survive in culture when fed diatoms possessing external threads (Thala8siosira, Cyclotella), but exhibited rapid growth rates when fed diatoms lacking threads (Minutocellws). The present study tested the hypothesis that the presence of marginal threads in small solitary centric diatoms renders them an unsatisfactory food for tintinnids. The data for tintinnids fed diatoms were compared to tintinnids fed small flagellates, dinoflagellates, and cyanobacteria to evaluate the relative food value of different phytoplankton species.

Materials and Methods Clonal cultures of phytopla nkton used in this study are listed in Table 1. Diatoms were selected for the presence of p-chitin threads (Thalassiosira, Cyclotellu), their absence (Minutocellu8), and presence of siliceous setae (Chaetoceros). Dinoflagellate, flagellate and cyanobacteria clones were axenic. Diatom c lones were trea t ed with antibiotics two weeks prior to the experiments. St ock cultures were grown in unbuffere d f / 2 medium (Gu/LLARD 1975) at 18- 20 °C under continuous illumination (90IlE . m- 2 • S-I). Media was pre pared according to VERITY (1984). Stock cultures were grown in 25 ml Pyrex test tubes or 125 ml flasks. Diatom clones were grown under two sets of conditions. One groups of c ultures was grown undisturbed ("stationary") a nd the other group was grown on a shaker table at ca. 1IiO rpm ("shaken") to retard development of external chitin threads (GIFFORD et a!. 1981). Clonal cultures of T i ntinnopsis acumi nflta DADA, and T intinnopsi8 vflsculum MEUNIER were initiated from isolations of individual tintinnids from Narragansett Bay. These species are representative summer-fall and winter-spring taxa, respectively. The same strain of eac h species w a s used in all experiments. Htock and e xperimental cultures were grown in polycarbonate tubes conta ining f/20 medium pre pared according to VERITY (1984). The phytoplankton species were selected on the basis of size so that they would be available to both T. vasculum (oral lori ca diameter - 45/Im) and '] '. acuminflt a (oral lorica diame ter - 20 11m). ~tock cultures of both tintinnids were fe d Isochrysis galbana . For each of the three experimental series (stationary diatoms; shaken diatoms; other phytoplankton), a known numbe r of tintinnids (1 - 5 per ml) of e a ch species was pipetted into duplicate polycarbonate tubes containing fresh m edium and recently transferred log-phase phytoplankton cells. Phytoplankton were offered at carbon concentrations (250 I'gC . 1-1) sufficient to support maximum tintinnid growth rates (VERITY 1984). The cultures containing phytoplankton Ilnd tintinnids were incubllted in continuous dim irracliance (5-10IlE . m - 2 • 5 - 1 ) at 18-20 °C for 3-4 d. EXllmination of cultures after each e xperiment indicated that the p- chitin threads did not regenerate, in agreement with GIFFORD et al. (1981). The e xperiments were conducted over 3-4 d to insure tha t changes in tintinnid abundance represented growth on available food and not a carryover effect. The cont ents of each tube were preserved with 1 % glut eraldehyde or 3 % buffered formalin; tintinnids were concentrat e!1 by settling to a volume of 5 m!. Two 1 ml aliquots of each settled concentrate were counted under phase contrast microscopy us ing a SEIlGWICKRAFTER chamber and a Zeiss Photomicroscope II. Changes in tintinnid abundance in each culture vessel were expressed as specific growth rate : II (doublings. <1- 1 )

=

(lIt) log2 (Ct/C o)

73

Tintinnid Food Preferences Table 1. Phytoplankton culture material Designation

Size (flm)

Source

CIUletoceros sp.

138

1000001Z

J. RINES; Narra. Bay, RI;

Cyelotella cf. easpil1

W7C

4---6

7/83 P. HARGRAVES; Narra. Bay, RI; 7/69

Cyelotella caspia GRUNOW

NB56 NB57

3-8 3-5

T. VILLAREAL; Narra. Bay, RI; 7/83

Cyclotella meneghiniuna KliTZ.

03A

5--10

Minutocellus polymorphus

675-<1

2-5

R. R. L. GliILLARD; Oyster Pond, MA; 6/56 R. R. L. GUILLARD; 06° 20' N, 54° 59' W; 6/65

NB9

4---10

13-1

3-4

3H

3-4

)JB54

2-6

Dun

7-10

R. UKELES

Nanno·O

1-2

L.PROVASOLI; 1964

Rsp

5--9

L. PROVASOLI; 1964

Species Class Bacillariophyceae

(HARG. & GliILLARD) HASLE, VON STOSCH & SYVERTSEN

Thalussiosira constricta GAARDER Thalas8iosira oceallica HASLE Thala88iosira pseudollana HASLE & HEDIDAL 1'halassiosira sp. Class Chlorophyceae DUllaliella tertiolecta B"CTCHER NUltllochloris oculata DROOP

T. VILLAREAL; Narra. Bay, RI; 1/83 R. R. L. GUILLARD; 33° II' N; 65° 15' W; 12/58 R. R. L. GUILLARD; Moriches Bay, NY; 9/58 T. VILLAREAL; Narra. Bay, RJ; 7/83

Class Cryptophyceae

Cryptomonas baltica (KARST>:!<) Bl;TCHER Class Cyanobacteriaceae Synechococcus bacilluria B';TCHER SYllechoeoccus sp.

Syn

R. R. L. GUILLARD; i\Iilford, CT; 1957

DC2

L. BRAND; 33° 45' N, 67° 30' W; 7/78

Class Dinophyceae

Gyrodillium €stuariale

G-7

7-10

Ht:LBlJRT

'v. GARDINER;

Hillsborough

Bay, FL 9/79

Heterocapsrt pigmrteft LOEBLICH, SCH)IIDT & SHERLEY

CP

8-12

)r.

Prorocentrum triestinum SCHILLER

~95B

8-14

P. HARGRAVES; Narra. Bay, RI; 9/ 69

BERNHARD; Ligurian Sea

Class Prymnesiophyceae Dicrateria inor/latrt PARKE Jsochrysis galbana PARKE

Dicrat

4---6

)1. PARKE; England

Iso

2-4

)r.

PARKE; England; lI38

PavlovlI lutheri (DROOP) GREEN

)fono

3-.'>

)r.

PARKE; Finland; 1951

Class PI'Hsinophyceae ol[icromollas sp.

DW8

I-Z

R. R. L. GnLLARD; 1964

74

P. G. VERITY and T. A. VILLAREAL

where Ct and Co were tintinnid abundances on days t and 0, respectively. Exponential growth was assumed (VERITY and ::iTOECKER 1982 ). Phytoplankton carbon concentrations within the experi. mental cultures were determined for each species by filt ering duplicate samples of known volume onto pre·combusted 0.45 11m Gelman A l E glass fiber filt ers. The filters were frozen, freeze.d ried, and stored over desiccant until analyzed. Phytoplankton carbon content was determined using a HP 185B CHN a nalyzer an d appropriate blanks (l'iHARP 1974). The range of dllplicat e carbon m easu rements was 10 % of the me an. Diatom species were identified from cleaned valves (SBro~SEN 1974) mount ed in Cumar. The occurr ence of /3.chitin threads (HERTH 1979) in the diatoms 'l'hul1l88iosirll and Cyclotella grown under stationary and shaken conditions was examined using light microscopy. The shadow·casting technqiue of QUACKENBUSH et al. (1980) was used to enhance the contrast betwcen threads and background, with the following modifications. Cells were rinsed with deionized water to remove salts and air· dried on alcohol·cleaned glass overslips. :Samples were shadowed with 3 mg of a lumi· nium wire at < 0.001 torr, and mounted on glass slides in Cumar. Valve diameter and thread length and number were measured on 25 cells encountered sequent ially. Valve diamet e r was measured to the nearest 0.5 micron and thread length to the nearest micron. A Zeiss Photomicro· scope II was used for all light microsco py and photomicrographs. Terminology describing compo· nents of the di a tom frustule follows ANONY~rOUS (1975) and Hoss et al. (1979). "Threads" and "fibrils" refer to the organic projections from the strutted processes of the diatom valves; specific terms for these structures are lacking. They are not spines, which refe r to specialized siliceolls struc· tures (ANONYMOUS 1975).

±

Results Mean valve diameters of diatoms were not significantly different in stationary and shaken cultures (Table 2; p < 0.05). Valve diameter ranged from 2,um (M£nutocell'l.U1) to ll,um (Cha etoceros). Significant external projections were not found in M£nutocellus and therefore the total cross-sectional and valve diameters were equivaJ.ent. Setal length of Chaetocer08 sp. ranged from 28-114pm with a mean of 69 pm (total cross-sectional diameter = 148,um). Significant differences between stationary and shaken cultures in length and number of setae in Chaetoceros were not observed. Table 2. Mean valve diameter and total cross·sectional diameter (± standard deviation) of diatoms grown under sta tionary and shaken conditions. Cross·sectional diameter was calculated as (valve diameter + (2) thread length). Differences in valve diameter and eross·sectional diameter between stationary and shaken cultures were tested using a two·tailed t·test (p < 0.05; NS = not significant) Species

Minutocellu8 polymorphus T hala811ioBira p8eudonanu ThalasBiosira oceanica

Desig. nation

Valve Diameter (,urn) Stationary

Shaken

Cross·section (pm) p

Stationary

Shaken

p

675-d

2.3 (0.4)

2.3 (0.3) NS

2 (0)

2 (0)

NS

3H

3.2 (0.5)

2.7(0.4) NS

39 (15)

4 ( I)

0.05

13-1

3.5 (0.8)

3.8 (0.8) NS

38 (9)

8 (5)

0.05

Thalas8io8ira cOll8tricta NB9

7.3 (1.2)

7.7(1.5) NS

58 (9)

Thala88io8ira sp. Cyclotella cU8piu Cyclotella cU8pia Cyclotella cf. ca8pia

NB54

6.0 (l.I)

4.8 (0.8) NS

49 (13)

15 (8) 14 (9)

0.05

NB56

5.7 (0.8)

5.2 (1.2) NS

54 (II)

NB57

4.8 (1.0)

5.1 (1.1) NS

W7C

5.2 (1.2)

Cyclotella meneghiniana 03A Chaetoceros sp. 138

0.05 0.05

48 (II)

10 (6) 11 (6)

4.2 (l.I) NS

79 (23)

39 (22)

NS

8.4 (1.5)

8.8 (1.9) NS

67 (27)

38 (26)

NS

10.5 (2.4)

10.7(2.8) NS

148 (41)

I:n (52)

NS

0.05

75

Tintinnid Food Preferences

Figs. 1-2. Thalassiosira constricta, elone

~B9.

Fig. 1. T. constric/a grown IIn
Oil R

shake r tablt-', with ft'Wl'r and short /' r thre ads . :'icalt, bars

~

IOllm.

All clones of 1'halussiosira (n = 4 species) and Cyclotella (n = 4 species) produced extensive threads when grown under stationary conditions (Table 2; Fig. 1). Mean thread length ranged from 15,um (ThaLassios~·ra oceanica) to 37,um (CyclotelLa cf. cuspia) , resulting in eross-settional diameters of 33,um and 79,um, respettively. When the cultures of 'l'/talwJsiosira and Cyclotellu were shaken, substantial reductions in thread length (Fig. 2; Table 2) and nUl\lber occurred (Fig. 3). Average thread length was l,urn and 2,uIll, respettively, resulting in cross-sectional diameters of 4,um and 8,urn under shaken conditions. 1'h((lussios~·ra sp., 1'halassiosira constricta, and Cyclolella caspia (2 dones) had average <.Toss-sectional diameters of 1O-15,um. Cyclotella d. caspia and Cyclotella meneghiniuna exhibited the longest threads under stationary conditions and also showed the longest mean thread length under shaken conditions; cross-sectional diameters were :l8-39,um. Fewer threads were observed in diatoms grown on the shaker tabl e, with the majority containing 0-3 threads per cell; cells cultured under stationary conditions contained 5-10 times more threads (Fig. :l). Tintinnopsis 1'Uscul1(m grew at a rate of 1.:J doublings . d- l when fed M1:n1tiocelll1s cultured under stationary conditions (Table 3), similar to that observed when fed Isochrysis (1.6 doublings . d- 1 ). Lowered growth rates (0.4-0.5 doublings . d- 1 ) occured when fed the two slllallest Thalassiosira species. Mortality was observed when T. vasculum was fed the larger thread-containing species. Decreased thread length in shaken cultures of the eight thread-containing species was associated with significant (p < 0.05) increases in T. vasculum growth. Growth rates for T. VClsculum fed 'J'hulassiosira oceanica (l.4 dou blings . d-1 ) and Thalussiosira psel1donana (1.5 doublings . d- 1 ) were indistinguishable from those observed when fed Minl1tocell118 and Isochrysis (l.5 doublings· d- 1 ). Growth rates of 0.7-1.0 doublings . d-1 were observed for tintinnids fed Thalassiosira sp. , Thalassiosira constricta, and Cyclotella caspia. T. vasculum showed the lowest growth rates (0.3- 0.4 doublings . d-1 ) when fed species with the largest cross-sectional diameter, Cyclotella meneghiniana and Cyclotella d. caspia. T. vasculum did not survive when fed Chaetocero8 sp. cultured under stationary and shaken conditions.

76

P. G.

VERITY

and T. A.

VILLAREAL

100

A

80 60

..... .....

40

::?

20

~

0

~

lI..

~

B

"11)

.....

80

~ ~

60 40 20

o~-L~~~~~~~£illw£~ 0-1 4-5 8-9 12-13 16-1720-21 24-25 28-29 THREAOS (NO·CELC')

Fig. 3. Frequency histogram of thread number in cells grown under stationary (hatched bars) and shaken (open bars) conditions. A: Thalflssiosim constricta. B: Cyclotella meneghiniana.

Tintinnopsis acuminata grew at 1.8-2.2 doublings . d- 1 when fed Isochrysis and Minutocellus (Table 4). Growth did not occur when fed any of the thread-bearing diatoms from stationary cultures. When the threads of five of the eight thread-bearing species were reduced by shaking, T. acuminata ex hihited significant increases in growth rates. Growth rates achieved when fed the two smallest Thalassiosira species, T. oceanica and T. pseudonana,\were similar to those observed when fed Minutocellus. Thalassiosira sp., Thalassiosira constricta, and Cyclotella caspia cultured under shaken conditions supported low growth rates of T. acuminata, similar to responses by Tintinnopsis vasculum. T. acuminata fed Cyclotella cf. caspill, Cyclotella meneghiniana, and Chaetoceros sp. taken from both stationary and shaken cultures did not survive. Decreases in relative growth rate of T. t'asculum and T. acuminata accompanied increasing cross-sectional diameter of their food (Fig. 4). T. vasculum and T. acuminata grew when fed diatoms with a cross-sectional diameter up to 87 % and 75 %, respectively, of its orallorica diameter. Neither tintinnid grew when fed diatoms whose cross-sectional diameter exceeded the oral lorica diameter. Funetional regression of. tintinnid growth rate (fl , doublings· d- 1 ) on cross-sectional diameter (CSD, flm) of shaken diatom cultures yielded: T. vasculum T. acuminata

fl = 1.43 - 0.03 (CSD), r2 = 0.84, P fl = 1.95 - 0.11 (CSD), r2 = 0.86, P

< 0.05

<

0.05.

Growth rates of tintinnids fed several flagellate, dinoflagellate, and cyanobacteria species are given in Table 5. Isochrysis galbana and DiCtateria inornata supported the highest growth rates of both T1'ntinnopsis t'asculum (1.6-1.8 doublings· d-l ) and

165 190

02 ) 01 )

211 184

NB9

NB54

2) =

> 50% mortality 100 % mortality

1.0 (0.9-1.2)

266

0_5 (0.5-0.5)

288

13-1

I) =

0.9 (0.6-1.1)

268 274

1.3 (1.2-1.5) 0.4 (0.3-0.6)

209 217

0.4 (0.4-0.5) 212 240

02)

02)

193 245

W7C

03A

138

0.3 (0.3-0.3) 267

02)

318

NB57

02 )

0.9 (0.8-1.0)

220 285

0 1) 01)

243 357

NB56

0.7 (0.7-0.7)

1.4 (1.3-1.5)

1.5 (1.1-1.8)

1.5 (1.3-1.7)

NS NS 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 NS

675·d 3H

232

1.5 (1.3-1.7)

1.6 (1.4-2.0)

p

It (range) (d . II-I)

247

Shaken C (/lgC . I-I)

Iso

ji (range) (d . d- I )

lsochrysis ga/bana Minutocellus polymorphus Thalassiosira pseudonana Thalussiosira oceanica Thalassiosira eonstrieta Thalassiosira sp. Cye/otella caspia Cyclotella easpia Cye/otella cf. easpia Cyclotella meneghiniana Chaetoceros sp.

Stationary C (/~gC . I-I)

Designation

Species

Table 3. Mean anel range of growth rates (cloublings . day-I) of Tintinllopsis vasculum fed 18oehrys18 anel e1iatoms grownumler stationary ami shaken conditions. C = phytoplankton concentration Statistical tests as in Table 2.

-:J -:J

III

"'"

::l

'"

...>'d ~ ...'"

p.

0 0

""J

0:

::l

5' "'5'"

.."

1) = > 50 % mortality =.100 % mortality

2)

0.05 0.05 0.05

0.6 (0.4-0.7) 0.8

0.5 (0.3-0.6) 02) 02) 02)

230 252 271 234 214 309 280

02) 02) 02 ) 02) 02) )

2

02)

283 275 272 204 269 230 265 247

13·1 NB9

NB54

NB56

NB57

W7C

03A

138

0

0.05

1.4 (1.2-1.5) 0.3 (0.1-0.5)

245

0 1)

376

3H

NS

NS

NS

0.05

0.05

1.4 (1.3-1.5)

280

02)

(0.~1.0)

NS

1.6 (1.5--1. 7)

NS

2.0 (1.9-2.2)

228 216

1.8 (1.~2.0)

2.2 (2.0---2.4)

p

190

ji, (range) (d . d- 1)

250

C (pgC. 1-1)

Shaken

ji, (range) (d . d-1)

675·d

I soehrysis galbana Minutocellus polymorphus Thalassiosira pseudonana Thalassiosira oceanica T halassiosira constricta Thalassiosira sp. Cyelotella caspia Cyclotella caspia Cyelotella ~f. caspia Cyelotella meneghiniana Chaetoeeros sp.

Stationary C(pgC. 1-1)

Iso

Designation

Species

Table 4. ::\reall and rnnge uf growth rates (doublings . day-I) of Tintinnopsis acuminata fed Isoehrysis and diatoms grown under stationary and shaken conditions. C = phytoplankton concentration Statistical tests as in Table 2

t"

:.-

i'l

:0

:.-

t"

t=:

?-<

~

"-

::l

il'

><

i:l>-3

~

P L?

00

'J

79

Tintinnid Food Preferences

100

••

80 60

•• • •

40

.....

20

*

0

~

100

'-

e:

'\

A

0()

80

-.

60 40

~

0

0

B

••• •

0

i

•

20

a:> 00

0 0


10

20

30

40

50

60

0

0

70

80

90

CSD (pm) Fig. 4. Helative growth rates of T intinnopsis acuminatn (A) and 'i'intinnopsis vasculum (B) as a function of mean cross· sectional diameter (CSD) of cells c ultured under stationary (0) and shaken (.) conditions. Tintinnid growth rate on each diatom species (/1) is expressed as a percent of growth on Minutocellus (pM).

Tintinnopsis acu1ninala (2.3-2.4 doublings . d- 1 ). T. vasculu1n grew well when fed lutheri and Cryotomonas baltica (1.3 doublings . d-1 ) ; slower growth rates were found on the small Nannochloris oculata and Micromonas sp. (0.9-1.0 doublings· d- 1 ). T. acuminata grew equally well on P.lutheri, N. oculuta, and Micromonas sp. (1.6-1.9 doublings· d- 1 ). Tintinnid growth rates were lowest when fed Dunaliella tertiolecta. T. vasculum exhibited growth rates of 0.5-0.9 doublings . d- 1 when fed dinoflagellates, whereas T. aC71minala did not grow on dinoflagellates. Neither species survived on cyanobacteria. Pa1~'lova

Discussion Tintinnopsis did not grow, or exhibited reduced growth rates, when fed threadbearing diatoms, but grew rapidly on diatoms lacking threads or having reduced threads. Growth rates were inversely related to effective cell size, suggesting that the reduction of thread size and number, rather than any cellular biochemical changes associated with the process of thread removal, was responsible for these growth rates. Thread extrusion through strutted processes is a common feature in the genus Thalassiosira (FRYXRLL and HASLE 1972 ; SYVERTSEX and HA SLE 1982), and probably occurs in all centric diatoms with strutted processes (HASLE 1972). The experimental results suggest that the low growth rates of natural tintinnid populations during blooms

DW8

l'rasinophyceae lvlicromona8 sp.

1) = > 50 % mortality 2) = 100 % mortality

Dicrat Iso Mono

G-7 CP N95B

Syn DC2

Rsp

Dun Nanno-O

Designation

Dicrateria in-ornata I sochryBi8 galbana Pavlova lutheri

Prymnesiophyceae

Gyrodinium estuariale Heterocapsa pigmaea Prorocentrum tries/i num

Dinophyceae

Synechoooccus bacillari8 Synechococcus sp.

Cyanobacteriaceae

Cryptomonas baltica

Cryptophyceae

Dunaliella tertiolecta N annochlori8 oculata

Chlorophyceae

Species

225

237 248 209

196 265 267

181 165

291

286 204

C(f1gC' I-I)

T. va8culum (range) (d . d- I )

0.9 (0.7-1.1)

1.8 (1.6-2.0) 1.6 (1.5-1.7) 1.3 (1.0-1.7)

0.9 (0.7-1.0) 0.5 (0.4-0.6) 0.7 (0.5-0.8)

02 ) 02 )

1.3 (1.1-1.5)

0.3 (0.2-0.5) 1.0 (0.8-1.2)

Ii

196

253 295 222

214 283 268

189 169

251

187 195

C (f1gC . I-I)

T. acuminata (d, d- I )

1.6(1.4-1.8)

2.3 (2.0-2.6) 2.4 (2.3-2.6) 1.8 (1.6-1.9)

01 ) 01 )

01 )

02) 02)

1.0 (0.8-1.2)

0.5 (0.2-0.8) 1.9 (1.8-2.0)

Ii (range)

Table 5. Mean anc! range of growth rates (doublings· day-I) of Tintinnopsis vasculum and Tintinnopsis acuminata fed various phytoplankton species. C = phytoplankton concentration

\0

t"'

II>

l'l

~

II>

t"' t"'

:::

>

~

Q.

::l

><:

OJ

~

~

p < l'l

~

Tintinnicl 1<'00(1 Preferences

81

dominated by Thala88io8ira con8iricta (Vl.;RITY 1984) are probably due to the chitin threads of these phytoplankton. Although ingestion rates were not directly measured, positive growth rates require ingestion and assimilation of food. Decreased tintinnid growth rates when fed diatoms bearing threads illlplies decreased ingestion, rather than reduced assimilation efficiency. For ciliates, the latter alternative would imply that, food vacuoles pass so rapidly through the body that phytoplankton cells are not digested. Examination using phase microscopy of Tintinnop8~'8 fed thread-bearing diatoms showed few digestive vacuolcs, suggesting that the presence of threads on solitary centric diatollls reduced grazing by these tintinnids. BLACK BOURN (1974) reported that Pavella 8errata MOBU:S (J0RGENSEN) and EutintinnU8latu8 J0RGENSEN ingested 'J'lwlassio8ira pseudonana. Since the oral lorica diameter of these tintinnids was ca. 70,um (KOFOID and CAMPBELL 1929), the presence of threads apparently had little effect on such large tintinnids. In the present study, the larger Tintinnop8i8 t'((8culum (oral lorica diameter = 45,ulll) exhibited positive growth rates when fed T. p8eudonana, while the smaller T. acuminata died when fed this species. Thus, the presence of threads rna.;: have different effects depending on the relative sizes of predator and prey. GIFFORD et al. (1981) found higher grazing rates by the marine calanoid copepod Calanu8/inmarchicus on Thala881'o8ira u'eis8/logii bearing threads than on cells lacking threads. They attributed the difference to the larger effective size of thread-bearing cells, which facilitated their capture by filter-feeding copepods. Thus threads apparently impede cell ingestion by small ciliates but increase their vulnerability to predation by larger herbivores. SPITTLER (197:l) and HEINBOKBL (1978 b) observed that the largest particle size ingested by tintinnids feeding 0:1 a range of food particles averaged 40-45 % of their orallorica diameter. The Tintinnop8i8 species examined here exhibited positive growth rates when fed diatoms in which the average cross-sectional diameter exceeded 50 % of the tintinnid oral lorica diameter. This apparent discrepancy suggests that the upper size limit of prey may be flexible when smaller food is not available, or that average cross-sectional diameter is only a relative measure of their availability as food. CAPRIULO (1982) reported that tintinnids collected from Long Island Sound ingested particles as large as 100 % of their oral lorica diameter. Since phytoplankton concentrations in the present study were 2-3 times higher than the minimum food levels which saturated growth (VERITY 1984), Tintinnop8i8 may have ingested sufficient numbers of cells with short threads to support growth. Such an effect would be more apparent as average cross-sectional diameter decreased, in agreement with observed responses. The prynmesiophytes, Dicrateria, 18ochrY8i8, and Pavlova, supported tintinnid growth rates as rapid as those of TintinnOp8i8 fed Minutocellu8; Cryptomona8 and Micromonas were also good food organisms. These flagellates were generally preferred food species for other coastal tintinnids (BLACKROURN 1974; JOHANSEN 1976; HEIBOKEL 197Ra). However, all small flagellates were not equally good food items. DUII((hella was rapidly ingested in grazing experiments (BLACKBOURN 1974; JOHANSEX 197fi), whereas growth rates of 1\ntinnop8£8 were very low when fed this species. HEIXBOKEL (1978a) also reported that J.~ochry8i8 was a better food than Dunaliella for tint innids. r n addition, Dunal£ella is a poor food for planktonic ciliates in the genus StrolJlbidium (D. GIFFORD, pers. COmll1.), juvenile clams and oyster sprat (WALNE 1(70), and the marine cope pod Acal't7'a [onsa (TOMAS and DEASON 1981). These responses may reflect the unusual fatty acid composition of this organism (LANGDON and WALDOCK 19RI). Roth Tinlinnopsi8 species exhibited 100 % mortality when fed chroococcoid cyanohactcria. Since tintinnid mortality due to starvation occurs within three days at (\

Arch. Protistenkd. 1\<1. 1:11

82

P. G. VERITY and T. A. VILLAREAL

10°C (VERITY and STOECKER 1982), and tintinnids are capable of ingesting bacteriasized particles (HOLLIBAUGH et al. 1980), the absence of growth when fed Synechococcus apparently represented nutritional inadequacy. Cyanobacteria pass undigested through the guts of some marine copepods (JOHNSON et al. 1982), and are also an unsuitable food for freshwater daphnids (LAMPERT 1981) and marine c:iliates of the genus Strombidium (D. GIFFORD, pers. comm.). The Tintinnopsis species differed in their responses to dinoflagellates as a food source. T. vasculum exhibited moderate growth when fed dinoflagellatcs, whereas the smaller T. acuminata did not grow when fed Gyrodinium, Heterocapsa, and Prorocentrum. STOECKER et al. (1981) reported that the large tintinnid, Favella sp., was a specialized predator on dinoflagellates. BLACKBOURN (1974) found that the largest food particles in the guts of Fa'L'ella serrata and Eutintinnuslatus were usually dinoflagellates. These combined data suggest that dinoflagellates may be an important dietary component predominantly for larger tintinnids. BLACK BOURN (1974) rarely observed diatoms in the gut contents of field-collected tintinnids, and speculated that these phytoplankton were too large to contribute significantly to tintinnid diets. The experimental data indicate that, in the absence of external projections such as threads and setae, diatoms are a good food for tintinnids. The presence of threads and setae increases the effective size of diatoms and reduces growth of tintinnids, apparently by impeding ingestion. This suggests that valve diameter is not nec:essarily an accurate measure of cell size in an ecological context. In addition, small phytoplankton cells lacking external projections vary in nutritional value. Small diatoms such as Minutocellus and small flagellates such as Dicrateria and isockrysis support rapid tintinnid growth rates, whereas small cyanobacteria containing phycoerythrin (clone DC2) and phycocyanin (clone Syn) are nutritionally inadequate. The chlorophycean flagellate Dunaliella is a poor food, and the chrysophycean flagellate OlisthodiscU8 luteu8 CARTER inhibits tintinnid growth at low concentrations and is toxic at bloom concentrations (VERITY and STOECKER 1982). Thus, both size and food quality are important factors influencing tintinnid growth rates.

Acknowledgements W. GARDINER, R. R. L. GUlLLARD, P. E. HARGRAVES, J. RINES, and T. J. S~rAYDA supplied cultures. H. E. KOSKE provided the shaker table and T. J. SMA VDA the laboratory facilities. D. SCALES and P. E. HARGRAVES supplied technical assistance in shadow· casting samples. N. HAIRSTON, Jr., P. E. HARGRAVES, S. LEVINGS, J. MeN. SIEBURTH, and T. J. SMAYDA offered valuable comments on an early draft. This work was supported by Department of Commerce (NOAA) Grant No. NA80 HA·D00064 awarded to T. J. S)[AVDA.

Literature ANONV)WUS (1975): Proposals for a standarciization of diatom terminology and diagnoses. Nova Hedw., Beih. 53: 323-354. BERK, S. G., BROWNLEE, D. C., HEINLE, D. R, KLING, H. J., and COLWELL, R. R. (1977): Ciliates as food sources for marine planktonic copepods. :Microb. Ecol. 4: 27-40. BLACKBOURN, D. J. (1974): The feeding biology of tintinnid Protozoa and some other inshore microzooplankton, 224 pp. Ph.D. Thesis, Univ. British Columbia, Vancouver, B.C. CAPRIULO, G. M. (1982): Feeding of field collected tintinnid microzooplankton on natural food. Mar. BioI. 71: 73-8f\. ·FENCHEL, T. (19fi8): The ecology of marine microbenthos. II. The food of marine benthic ciliates. Ophelia 5: 73-121.

Tintinnid Food Preferences

83

FRYXELL, G. A ., and HASLE, G. H . (1972): 'l'halassiosim eccentric(t (EIIRENB .) CLEVE, T. symmetrico sp. nov. and some related centric diatoms. J. Phycol. 8: 297-317. FL"RNA~, 2'11. J. (1982): Growth rates of s limmer nanoplankton « 10 11m) populations in lower Nar)'agansett Bay, l{horie Island, U:-iA. }lar. BioI. 70: 105- 115. GIFFOll.D, D. ;J., BOHRER, H. W ., and BOYD, C. 2'11. (1981): :-ipines on diatoms: do cope pods care? Limnol. Oeeanogr. 26: 1057-HHi2 . GOLD, K . (1971): Growth characteristics of the mass-reared tintinnid Tintinnopsis beroidea. )Iar. BioI. 8: 105-108. - (19i3): ~Iethods for growing Tintinnida in continuous cllltlll·e. Amer. Zool. 13: 203-208_ GRAr--, H . H . (1912): Pelagic plant life. In: MURRAY, J., and J . HJORT (ed.), The depths of the ocean, pp. 307 -3SH. London. GUILLARD, H. H. L. (1975): Culture of phytoplankton feeding marine invertebrates. In: 8){JTH, W. L., and }1. H. CHA!\LEY (pd.), Culture of marine invertebrates, pp. 29-60. New York. HA SLB, G. H. (1972): Thalflssiosil"ll subtilis (Bacillariophyceae) and two allied species. Xorw. J. Bot. 19: 111-137. HEINBOKEL, J. F. (1978a): :-itllclies on the functional role of tintinnids in the Southern California Bight. 1. Grazing and growth rat cs in laboratory cultures. ?Iar. BioI. 47: 177-189. - (1978 b): :-;tudics on the fun ct ional role of tintinnids in the l:iouthern California Bight. II. Grazing rates of field populations. )far. BioI. 47: 191-197. Ht:RTH, W. (1979): The site of /i-chitin fibril formation in centric diatoms. II. The chitin-forming cy toplasmic structllres. J. Ultrastr. Hes. 68: lfi-27. HOLLIBA(;GH,.J. T., FUHR)!AN, J. A., and AZA)!, F. (1980): Hadioactively labelling of natural assemblages of bacterioplankton for use in trophic studies. Limnol. Oceanogr. 25: 172- 181. JOHANSEN, P. L. (1976): A st lldy of tintinnids and other Protozoa in eastern Canadian waters, with special refcrence to tintinnid feeding, nitrogen excretion, and re productive rates, 156 pp. Ph.D. Thesis, DalhollsieCniv., H a lifa x, N.S. JOHNSON, P. L., X IT, H.-~., and SIEBURTII, J. MCN. (1982): The utilization of chroococcoid cyanobacteria by marine protozoopl ankters but not by calanoid copcpo(is. Ann. Inst. Oceanogr. Paris 58 (~), 297-308. Km"ow, C. A., and CA~lPBELL, A. S. (1929): A conspectus of the marine and freshwater Ciliata belonging to the suborder Tintinnoidea, with descriptions of n ew species, principally from the Agassiz Expedition to the eastern tropical Pacific, 1904- 1905. L'niv. Calif., Berkeley, Pub!. Zoo I. 34: 1- 403. L.~)IPERT, \V. (1981): Inhibitory and toxic effects of blul'green algae on Daphnia. Int. H<:v. ges. Hydrobiol. 66: 285-298. LANGDON, C. J ., and \VALDOCK,M . J . (1981): The effect of algal and artificial diets on the growth and fatty acid composition of Cras80strea gigU8 sprat. J. mar. bioJ. Ass. V.K. 61: 431- 448. NrvAL, P., and NIVAL, S. (1976): Particle retention efficiencies of an hc rbivorous copepod, AClIrtia clausi (cop"podite and adult stages): effects on grazing. Limno!' Occanogr. 21: 24-38. PARSONS, T. R., and L:EBRASSEUR, R. J. (1970): The availability of food to different trophic levels in the marine food chain. In: J. H. /STEELE (ed.), ?Iarine food chains, pp. 325-343. Edinburgh. PORTER, K. G., PACE, M. L., and BATTEY, J . F. (1979): Ciliatc protozoans as links in freshwater food chains. Nature 277: 5H3- 51i5. QUACKENBUSH, D. W., BOTHWELL,)1. L., and BISSON, P. A. (19S0): Aluminium shadowing _ direct projection photomicroscopy of diatom frustules. Can. J . Fish. Aquat. Sci. 37: IHiO-lHiH. ROBERTSO~, J. H. (1983): Predation by es tuarine zooplankton on tintinnicl eiliates. Est. Coast. Shclf Sci. 16: 27-3ti. Ross, R ., Cox, E. J., l\:ARAYEVA,~ . I ., ~IAXN, D . G., PADDOCK, T. B. B ., SUlONSEX, R., and Sn!s, P. A. (1979): An emended tcrminology for the siliceous components of the diatom cell. ~ova . Hedw., Beih. 64: 511-533. SHARI', J. H. (1974): Improvcd analysis for "particulate" organic carbon and nitrogen from seawater. Limnol. Oceanogr. 19: 984-989. SDIONSEN, R. (1974): The diatom plankton of the Indian Ocean Expedition of RV Meteor 1964-5_ )Iet,·or. Forschungsergeb. Reihe D. BioI. 19, 1-107_ SPITTLER, P. (1973): Fccding experiments with tintinnids. Oikos 15 (8): 128-132. 6'

84

P. G. VERITY and T. A. VILLAREAL, Tintinnid Food Preferences

STOECKER, D ., GUILT.ARD, R . H. L., and KAVEE, R. 1'11. (1981): Selective predation by P'avelill ehrenbergii (Tintinnida) on and among dinoflagellates. BioI. Bull. mar. bioI. Lab. Woods Hole 160: 13ti- 145. SYVERTSEN, E. E., and HASLE, G. H . (1982): The marine planktonic diatom Lauderia annulut(£ CLEVE, with particular reference to the processes. Bacillaria 5: 243- 250. TO~IAS, C. H., and DEASON, E. E. (1981): The influence of grazing by two Acartia species on OlisthodisclIsluteus CARTER. P .S.Z .N.I. l\[ar. Ecol. 2: 215- 223 . VERITY, P. G. (1984): The physiology and ecology of tintinnids in N arragansett Bay, Rhode Island, 432 pp. Ph.D. Thesis, University of Rhode Island, Kingston, RI. - and STOECKER, D. (1982): Eff.~c ts of OlisthoriiscIIsluteus on the growth and abundance of tintinnids. Mar. BioI. 72: 79-8 7. \VALNE, P. H . (1970): I:-ltuclies on thc food valllc of ninetee n genera of a lgae to juvenile bivalves of the genera Ostrea, Crassosl1'ecl, Mercell-aria, and Mytillls. Fish . Invest. 26: 1-62. Authors' address: Dr. PETER G . VERIT\" ancl TRAC\" A. VILLAREAL, University of Rhode Island, Graduatel:-lchool of Oceanography, Narragansett Bay Campus, Narragansett, Hhode Island 02882, FS.A.